The present invention generally relates to DC motors and more specifically to methods and apparatuses for driving brushless DC motors.
Modern appliances, such as HVAC systems, refrigerators and the like, typically include a number of devices controlled by brushless DC motors. A few examples of such devices includes fans for circulating air in a space, evaporator fans among others. Methods for driving the brushless DC motors include simple square wave control and other such methods, which typically generate a pulsating torque, and also a substantial negative torque. Such torque patterns generally result in large torque ripples, which typically excite mechanical resonance of motor housings and mechanically associated structures. This results in an undesirable audible noise and also leads to undesirable mechanical stresses in the motor components. The noise is particularly undesirable in air conditioning environments of homes, workplaces, vehicles and the like. Further, due to a negative torque component, average torque developed in the motor is decreased, thereby lowering the motor efficiency.
Accordingly it would be desirable to have methods and apparatuses to reduce the negative torque components and associated torque ripples in brushless DC motors, and thereby leading to less audible noise and vibrations emanating from motors.